An agricultural baler is a trailed machine (PTM—pulled type machine) used in agriculture for the purpose of creating bales of (typically) straw or other biomass such as hay, silage or similar crop material produced during a harvesting or mowing operation.
Various designs of balers have been proposed in the prior art. A common characteristic of virtually all balers is that they are most of the time towed behind agricultural vehicles such as tractors (or could be self-propelled). A baler includes an infeed via which biomass is ingested into the interior of the baler and compressed or otherwise treated to form bales. The completed bales are tied with twine or another lineal object to make them rigid and self-supporting, after which they are ejected via a discharge chute typically at the rear of the baler so as to fall or be placed on the ground behind the tractor/baler combination as it moves forwardly along a harvested field.
In a rectangular baler it is possible to adjust the bale density, as the baler includes a substantially cuboid bale-forming chamber. It is known in the art to construct the bale-forming chamber with one or more moveable walls. The positions of the walls can be adjusted so as to alter the volume of the bale-forming chamber and thereby squeeze the bale during its formation to a greater or lesser degree. If, as is commonplace in a baler, each charge or flake of ingested biomass is substantially of constant volume, causing a reduction in the volume of the bale-forming chamber in this way leads to the creation of higher density bales, and vice versa. This, in turn, provides an ability to control the densities of the formed bales.
In more detail, each charge introduced into the bale-forming chamber is, at the point of introduction, uncompressed or compressed to a relatively low level. It is moved along the bale-forming chamber by longitudinal strokes of a piston or plunger that reciprocates under the action of an attached arm that in turn is driven by a bell crank e.g. secured to a rotating member. Each stroke of the piston therefore compresses an amount of biomass against the biomass already available in the bale-forming chamber. In consequence, the density of the formed bale increases if the volume into which the biomass is swept is reduced as a result of adjustments of the positions of the walls of the chamber at locations “downstream” of the furthest point reached by the piston during its motion.
The dimensions of cuboid shaped bales, however, are substantially fixed, firstly because of the cross-sectional dimensions of the bale-forming chamber and secondly because the baler forms the biomass into identical bale lengths that are ejected via the discharge as substantially identical, individual bales.
In WO2010/100068 the need is disclosed for an approach to apply tension to a bale in a bale-forming chamber of an agricultural baler to enable control of the bale characteristics (in particular the length of bales, especially for small cuboid shaped bales, to facilitate efficiency of use of bale handling equipment) in a consistent way. As described therein, the thickness and density of the bale are directly influenced by the amount of crop material delivered to the plunger for each stroke thereof and the resistance applied to the bale being formed in the chamber behind the plunger. Resistance applied to the bale in the chamber is commonly controlled by variations in the size of the cross section of the chamber through which the crop material is being urged by the plunger, by adjusting the position of one or more of the chamber walls to vary the orifice through which the crop material is extruded. In most approaches, however, the width or height of the chamber is being reduced at a constant rate along the length of the chamber, which does not result in a consistent pressure on the bale, while in improved approaches (GB 972562, WO2010/100068) the bale chamber comprises two zones wherein the rate of change in cross-sectional area experienced by the bale travelling through the zones is different for those zones. Such realization provides increased resistance against which the plunger may compress the crop material to form the bale in a first zone while in a second zone just a sufficient pressure on the bale surface is maintained.
New generation high density balers, requiring systems as described above with a bend in the walls to provide enough resistance to enable the plunger to compact the crop material to higher density levels, however, face the problem of selecting the right bend, in particular the angle of those bends, especially as the use of the most aggressive baler configuration, suited for one type of crop material and certain crop conditions, might prove to be too high for other types of crop material and/or other crop conditions, resulting in discontinued operation of the system and even overloads thereof which may damage certain parts of the baler.
When looking in more detail to the problems faced with in the production of such high density bales, one observes the following. For high density baling, it is necessary to apply a profile of the highest pressure possible in the bale along the length of the compression chamber. Such high pressure profile is established by selecting the shape and orientation of one or more of the walls (side walls and/or top wall of the bale chamber). For example, concerning orientation, instead of a horizontal wall (for the top wall) or parallel with the length of the bale chamber (for the side walls), an inclination downward, or inward respectively is used. As discussed before, even more advanced approaches change the shape of a side by means of a bend, for realizing a higher inclination at the start of bale chamber, resulting in higher pressure (to compress more rapidly the crop material at the beginning of the compression cycle), and a more relaxed inclination at the end of the bale chamber, resulting in less pressure and hence bale relaxation. Again, it is to be noted that a suited pressure profile is necessary for obtaining bales with good density characteristics while avoiding too high a pressure on the plunger in order to avoid discontinued operation or breakage of one or more parts of the entire system. However, as in such high-density balers the pressure on the crop material is a lot higher than in conventional large rectangular balers, there is more slip in between the wall and the harvested material also. In order to keep the crop material inside the compression room (to obtain the maximum crop density), there is a need to increase the friction level on the walls, e.g. on the top and side walls.
While the prior-art approaches (inclined and/or bend based systems) are good attempts to realize a suited pressure profile on the bale, there is room for still better systems.